Beverage cans and cans for other products often employ can ends or lids which are secured to the can body after the can body has been filled. The terms can "end" and can "lid" are interchangeably employed herein. Typically, the can lids employ manually manipulated closure elements which are utilized by the consumer to obtain access to the beverage or other product in the assembled can.
It is very important that the lid or end structure be leak-proof so that the can contents remain wholesome and palatable. For this reason various testing procedures have been established to detect whether lids are leak-proof prior to assembly of the filled can. It is known, for example, to insert one or more lids into a fixture or device and then apply pressurized helium or other gas to a side of the can lid or lids. This is often a manual process. An associated gas detector employed in the device detects the passage of any gas through the can lid. Prior art arrangements of this nature are characterized by their relatively slow speed of use and only a very small percentage of lids from a batch or supply thereof can be efficiently and economically tested. On the one hand, such a small percentage sample can result in leaking lids being undetected altogether. On the other hand, detection of a leaking lid on a narrow or small percentage sample basis can result in rejection of the entire supply of lids subject to random test, a result which may not in fact be warranted.
Another prior art approach for testing can lids has been to employ a source of light at one surface of the lid and a light detector at the opposing surface thereof. While this approach has the merit of being faster than the gas test approach outlined above, use of light may not detect leaks in a can lid since light will not go around corners and some defective can lids may require precisely that if certain types of can defects causing leaks are to be detected.
The following patents are believed to represent the current state of the art in the field of the present invention and the patents disclose a number of arrangements for detecting leaks and flaws in various types of articles, including can lids: U.S. Pat. No. 3,674,160;, issued Jul. 4, 1972, U.S. Pat. No. 4,055,455, issued Oct. 25, 1977, U.S. Pat. No. 4,934,180, issued Jun. 19, 1990, U.S. Pat. No. 5,307,139, issued Apr. 26, 1994, U.S. Pat. No. 5,417,105, issued May 23, 1995, U.S. Pat. No. 5,111,684, issued May 12, 1992, U.S. Pat. No. 4,184,362, issued Jan. 22, 1980, U.S. Pat. No. 4,086,497, issued Apr. 25, 1978, U.S. Pat. No. 4,946,028, issued Aug. 7, 1990, and U.S. Pat. No. 3,633,406, issued Jan. 11, 1972.
The invention disclosed and claimed herein is not shown in the above-identified patents.